Thermal spray deposited environmental barrier coating

ABSTRACT

In one example, a method for forming an environmental barrier coating (EBC) on a substrate. The method may include heating a backside of a substrate using a furnace enclosure, wherein a frontside of the substrate is outside the furnace enclosure, wherein the heating of the backside of the substrate with the furnace enclosure heats the frontside of the substrate to a surface temperature by heat conduction from the backside of the substrate to the frontside of the substrate; and depositing an environmental barrier coating (EBC) on the frontside of the substrate via a thermal spray device while the backside of the substrate is heated using the furnace enclosure, wherein the surface temperature of the frontside of the substrate is selected to control at least one of a porosity of the deposited EBC or a weight percent of a crystalline phase in the deposited EBC.

TECHNICAL FIELD

The disclosure relates to techniques for forming environmental barriercoatings using thermal spray deposition.

BACKGROUND

Ceramic or ceramic matrix composite (CMC) materials may be useful in avariety of contexts where mechanical and thermal properties areimportant. For example, components of high temperature mechanicalsystems, such as gas turbine engines, may be made from ceramic or CMCmaterials. Ceramic or CMC materials may be resistant to hightemperatures, but some ceramic or CMC materials may react with someelements and compounds present in the operating environment of hightemperature mechanical systems, such as water vapor. Reaction with watervapor may result in the recession of the ceramic or CMC material. Thesereactions may damage the ceramic or CMC material and reduce mechanicalproperties of the ceramic or CMC material, which may reduce the usefullifetime of the component. Thus, in some examples, a ceramic or CMCmaterial may be coated with an environmental barrier coating, which mayreduce exposure of the substrate to elements and compounds present inthe operating environment of high temperature mechanical systems.

SUMMARY

In some examples, the disclosure described a method that comprisesheating a backside of a substrate using a furnace enclosure, wherein afrontside of the substrate is outside the furnace enclosure, wherein theheating of the backside of the substrate with the furnace enclosureheats the frontside of the substrate to a surface temperature by heatconduction from the backside of the substrate to the frontside of thesubstrate; and depositing an environmental barrier coating (EBC) on thefrontside of the substrate via a thermal spray device while the backsideof the substrate is heated using the furnace enclosure, wherein thesurface temperature of the frontside of the substrate is selected tocontrol at least one of a porosity of the deposited EBC or a weightpercent of a crystalline phase in the deposited EBC

In some examples, the disclosure describes a system that comprises afurnace including a furnace enclosure, wherein the furnace is configuredto heat a backside of a substrate using the furnace enclosure while afrontside of the substrate is outside the furnace enclosure; a thermalspray device; and a computing device configured to control the furnaceto heat the backside of the substrates using the furnace enclosure toheat the frontside of the substrate to a surface temperature by heatconduction from the backside of the substrate to the frontside of thesubstrate; and control the thermal spray device to deposit anenvironmental barrier coating (EBC) on the frontside of the substratewhile the backside of the substrate is heated using the furnaceenclosure, wherein the surface temperature of the frontside of thesubstrate is selected to control at least one of a porosity of thedeposited EBC or a weight percent of a crystalline phase in thedeposited EBC.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual and schematic diagram illustrating an examplesystem for forming an EBC on a substrate in accordance with an exampleof the disclosure.

FIGS. 2A, 2B, 3A, and 3B are conceptual schematic diagrams illustratingthe example substrate and furnace of FIG. 1.

FIG. 4 is a flow diagram illustrating an example technique for formingEBC on a substrate.

FIG. 5 is a conceptual and schematic diagram illustrating an examplearticle including an EBC on a substrate.

FIG. 6 is a photograph of an apparatus used for testing to evaluate oneor more aspects of some examples of the disclosure.

DETAILED DESCRIPTION

The disclosure describes systems and techniques for forming anenvironmental barrier coating (EBC) system using thermal spraydeposition, such as air plasma spraying. The EBC coating system may bedeposited on a substrate, such as a CMC substrate, that serves as acomponent of a gas turbine engine or other high temperature system.Thermal spray systems may be used in a wide variety of industrialapplications to coat such substrates with EBC systems to modify orimprove the properties of underlying substrate or component as a whole.Thermal spray systems may use heat generated electrically, by plasma, orby combustion to heat material injected in a plume, so that molten orsoftened material propelled by the plume contact the surface of thetarget. Upon impact, the molten or softened material adheres to thetarget surface, resulting in a coating.

EBC systems may be an important contributor to the success of CMCs in ahigh temperature system. For example, the coatings may be configured toprotect against oxidation, water vapor recession, and other deleteriousreactions from damaging the structural CMC, e.g., during operation ofthe high temperature system. In some examples, an EBC system may containa multilayered structure including a silicon-containing bond coat andrare-earth disilicate layer(s). The layers of the EBC system may bedeposited using a thermal spraying process, such as, air plasmaspraying. The silicon bond coat may be applied to the CMC first toprovide proper adhesion between the CMC and the overlaying layers of theEBC system as well as to prevent contaminates from propagating throughand attacking the CMC.

In some examples, the bond layer is porous and the EBC system isamorphous in nature upon deposition using thermal spraying. The porousnature of the bond coat may allow for ingress of oxygen through the bondcoat to the CMC substrate, which may degrade the structural integrity ofthe CMC. The amorphous nature of the EBC system may be unstable at hightemperatures. As a result, the amorphous EBC system may crystallize whenthe EBC system is subjected to high temperatures during the life of thecomponent, e.g., during operation of a gas turbine engine or other hightemperature system. The crystallization of the EBC system may cause theEBC and/or bond coat to no longer adhere to the CMC and flake off. Forexample, the transition from amorphous to crystalline structure overtime may also result in volumetric changes in the EBC system and, thus,internal stresses in the layer(s). In particular, as the EBC structurechanges from amorphous to crystalline, there may be shrinkage in theoverall volume. This may cause a build-up in stress in the EBC as wellas the silicon bond coat. Eventually, the build-up in stress reaches athreshold and causes a crack to initiate to relieve the stress state.

In some examples, thermal spray systems are configured to be enclosedwithin a furnace with a substrate to elevate the temperature of thesubstrate and surrounding environment during the thermal spraydeposition of an EBC. However, such systems may be relatively expensiveand complicated (e.g., in terms of manufacturability) and the hightemperature furnace environment may have deleterious effects on thethermal spray components.

In accordance with examples of the disclosure, systems and techniquesare described that include controlling the surface temperature of asubstrate frontside during the deposition of an EBC coating systemthrough backside heating of the substrate. The frontside of thesubstrate may define the surface of the substrate onto which thelayer(s) of the EBC system may be deposited via thermal spraying. Thetemperature of the frontside surface during thermal spraying of the EBCsystem layer(s) may be controlled by heating the backside of thesubstrate within a furnace enclosure. By controlling the temperature ofthe frontside surface of the substrate during thermal spray deposition,the porosity and/or amount of crystalline phase of the depositedlayer(s) of the EBC system may be controlled. For example, the weightpercent of crystalline phase in the deposited EBC layer(s) of the EBCmay be increased compared to instances in which backside substrateheating is not employed. Increasing the weight percent of crystallinephase reduces the internal stresses resulting from transition fromamorphous phase to crystal phase during operation of a high temperaturesystem, as less material is available to transition. As another example,the porosity of the deposited EBC layer(s) of the EBC may be decreasedcompared to instances in which backside substrate heating is notemployed. An increase in crystalline phase and/or decrease in porosityof the layer(s) of the deposited EBC system may promote increasedadhesion between the deposited EBC system and underlying substrate.

In some examples, the backside of a substrate may be located within theopening of a furnace enclosure with the frontside exposed outside of thefurnace enclosure to allow access to the frontside surface for thermalspraying of layer(s) of an EBC system. The furnace enclosure may definea heated internal cavity that directly heats the backside of thesubstrate and thus indirectly heats the deposition surface of thesubstrate frontside. By controlling the backside heating using thefurnace enclosure, the temperature of the frontside surface of thesubstrate may also be controlled. The furnace enclosure may be employedto heat the backside of the substrate and heat the backside before,during, and/or after thermal spraying of the layer(s) of the EBC system.

In some examples, the substrate may optionally be heated pre-depositionand/or post-deposition in the same furnace enclosure and/or anotherfurnace, e.g., to further control the microstructure and crystallinephase of the layer(s) of the EBC system. For example, controlling thetemperature and/or duration of a post-deposition heat treatment and/ortime may allow for a transition from amorphous to crystalline phase inone or more layers of the deposited EBC system as well as tailor themicrostructure of the layer(s) of the EBC system.

Some examples of the disclosure may allow for the formation of adesirable EBC system (e.g., in terms of amount of crystalline phaseand/or porosity of the deposited layer(s) of the EBC system) while onlyheating the substrate on the backside during the thermal spraying theEBC system on a substrate, e.g., as compared to the entire thermal spraydevice being located within a high temperature furnace environment withthe substrate. The systems and techniques described herein may includelocally controlled heating of the backside of the substrate such thatthe frontside surface being thermally sprayed is at a desired depositiontemperature. The deposition temperature of the substrate frontsidesurface may be selected to allow for a reduction in porosity, e.g., inthe silicon bond coat, and one or more additional EBC layers withrelatively high crystalline phase. Such porosity and crystalline phasecomposition may promote better adhesion between the EBC and CMC, e.g.,during the life of the coated substrate.

FIG. 1 is a conceptual and schematic diagram illustrating an examplethermal spray system 10 for depositing an EBC system on a substrateusing a thermal spray process that includes controlled heating of thebackside of a substrate during the thermal spray process. Thermal spraysystem 10 may be configured to deposit one or more layers of a coatingsystem on a substrate to form a coated article, such as article 66 inFIG. 5 which includes EBC system 68 on substrate 24, using a thermalspray process. As will be described below, in one example, thermal spraysystem 10 may be configured to deposit the one or more layers of acoating system using a plasma spray process, such as an air plasma sprayprocess. In an air plasma spray process, the plasma is sprayed in an airenvironment, e.g., as compared to a spraying in a vacuum or an inert gas(e.g., argon) environment. For ease of description, the operation ofsystem 10 will primarily be described herein with regard to article 66of FIG. 5 although other articles formed using system 10 arecontemplated.

As shown in FIG. 1, system 10 includes components such as furnace 12,enclosure 20 and a thermal spray device 22. Enclosure 20 encloses somecomponents of thermal spray system 10, including, for example, thermalspray device 22. In some examples, enclosure 20 substantially completelysurrounds thermal spray device 22 and encloses an atmosphere. Theatmosphere may include, for example, air, an inert atmosphere, a vacuum,or the like. In some examples, the atmosphere may be selected based onthe type (e.g., composition) of coating being applied using thermalspray system 10, the type (e.g., composition) of substrate 24, or both.Enclosure 20 also encloses substrate 24 and furnace 12.

Substrate 24 defines a substrate to be coated using thermal spray system10. In some examples, substrate 24 may include, for example, a substrateon which a bond coat, a primer coat, a hard coat, a wear-resistantcoating, a thermal barrier coating, an EBC system, or the like is to bedeposited. Substrate 24 may include a substrate or body of any regularor irregular shape, geometry or configuration. In some examples,substrate 24 may include metal, plastic, glass, or the like. Substrate24 may be a component used in any one or more mechanical systems,including, for example, a high temperature mechanical system such as agas turbine engine.

Thermal spray device 22 is coupled to a gas feed line 26 via gas inletport 28, is coupled to a spray material feed line 30 via material inletport 32, and includes or is coupled to an energy source 124. Gas feedline 26 provides a gas flow to gas inlet port 28 of thermal spray device22. Depending upon the type of thermal spray process being performed,the gas flow may be a carrier gas for the coating material, may be afuel that is ignited to at least partially melt the coating material, orboth. Gas feed line 26 may be coupled to a gas source (not shown) thatis external to enclosure 20.

Thermal spray device 22 also includes a material inlet port 32, which iscoupled to spray material feed line 30. Material feed line 30 may becoupled to a material source (not shown) that is located external toenclosure 20. Coating material may be fed through material feed line 30in powder form, and may mix with gas from gas feed line 26 withinthermal spray device 22. The composition of the coating material may bebased upon the composition of the coating to be deposited on substrate24, and may include, for example, a metal, an alloy, a ceramic (e.g., anoxide-based ceramic), or the like.

Thermal spray device 22 also includes energy source 34. Energy source 34provides energy to at least partially melt the coating material fromcoating material provided through material inlet port 32. In someexamples, energy source 34 includes a plasma electrode, which mayenergize gas provided through gas feed line 26 to form a plasma. Inother examples, energy source 34 includes an electrode that ignites gasprovided through gas feed line 26.

As shown in FIG. 2, an exit flow stream 38 exits outlet 36 of thermalspray device 22. In some examples, outlet 36 includes a spray gunnozzle. Exit flow stream 38 may include at least partially meltedcoating material carried by a carrier gas. Outlet 36 may be configuredand positioned to direct the at least partially melted coating materialat substrate 24.

Thermal spray system 10 also include furnace 12. As shown in FIG. 1,furnace 12 includes an outer furnace enclosure 14 that defines internalcavity 16 that is heated during operation of furnace 12. Backside 40 ofsubstrate 24 is exposed to internal cavity 16 of furnace enclosure 14 toallow for direct heating of backside 40 of substrate 24 by furnaceenclosure 14 by radiation, convection, conduction, or combinationsthereof. The heating of backside 40 of substrate 24 heats frontsidesurface 42 of substrate 24 by conduction of heat through a thickness ofsubstrate 24. By controlling the heating of backside 40 of substrate 24,the temperature of frontside surface 42 may be controlled, e.g., duringdeposition of one or more layers of EBC system 68 of article 66. As willbe described further below, the temperature of frontside surface 42 maybe controlled by controlling the heating of backside 40 to control,e.g., increase, the amount of crystalline phase in the one or morelayers of EBC system 68 deposited on frontside surface 42 by thermalspray system 10. The porosity of the one or more deposited layers of EBCsystem 68 may additionally or alternatively controlled, e.g., decreased,by controlling the temperature of frontside surface 42 via heating ofbackside 40 of substrate 24 during the deposition process.

Furnace 14 may be any suitable furnace, such that it can achieve thetarget crystallization temperature. Furnace 14 includes a heat sourcethat allows for the controlled heating of furnace enclosure 16. Heatsource 14 may include one or more suitable heat sources such asmoly-disilicide and/or carbide heating elements, although other types ofheat sources are contemplated. Furnace 14 may include temperature sensor44, which senses the temperature within furnace enclosure 16, e.g., toprovide feedback to computing device 18 or another controller thatcontrols the temperature of furnace enclosure 16. Additionally, oralternatively, system 10 may include one or more sensors liketemperature sensor 14 configured to sense the temperature of backside 40and/or frontside surface 42 of substrate, e.g., to control thetemperature of frontside 42 during thermal deposition of coating 66 bythermal spray system 10.

Computing device 18 may be configured as a control device that controlsthermal spray system 10 to operate in the manner described herein.Computing device 18 may be configured to control operation of one ormore components of thermal spray system 10 automatically or undercontrol of a user. For example, computing device 18 may be configured tocontrol operation of thermal spray device 22, gas feed line 26 (and thesource of gas to gas feed line 26), material feed line 30 (and thesource of material to material feed line 30), and the like. For example,computing device 18 may be configured to control at least one of atemperature, a pressure, a mass flow rate, a volumetric flow rate, amolecular flow rate, a molar flow rate, a composition or aconcentration, of a flow stream flowing through thermal spray system 12,for instance, of gas flowing through gas feed line 26, or of exit flowstream 38, or of material flowing through material feed line 30.

Computing device 18 may be communicatively coupled to the components ofthermal spray device 22 and furnace 14 using respective communicationconnections. Such connections may be wireless and/or wired connections.While computing device 18 is shown as a single device, in otherexamples, computing device 18 may be more than one computing device,such as, e.g., where each of furnace 14 and thermal spray device 22 arecontrolled by different computing devices.

In some examples, computing device 18 may be configured to control thetemperature of furnace 12, e.g., before, during, and/or after thedeposition of EBC system 68 on substrate 24. As described herein, theheating of backside 40 with furnace enclosure 14 may heat frontside 42of substrate 14. During the deposition of one or more layers of EBCsystem 68, frontside 42 may be heated via heating of backside 40. Bycontrolling the temperature of frontside 42 during the deposition of theone or more layers of EBC system 68, the amount of crystalline phaseand/or porosity of the one or more layers of EBC system 68 may becontrolled. For example, the temperature of frontside 42 may becontrolled by heating of backside 40 to provide for a relatively highamount of crystalline phase (e.g., at least about 50 wt %, at leastabout 70 wt %, or at least about 90 wt % crystalline phase) in the oneor more layers of EBC system 68 and/or a relatively low porosity (e.g.,less than about 10% porosity, such as less than about 5% porosity, about1% to about 10% porosity, about 1% to about 5% porosity, orsubstantially no pores) in the one or more layers of EBC system 68.

Computing device 18 may include, for example, a desktop computer, alaptop computer, a workstation, a server, a mainframe, a cloud computingsystem, or the like. Computing device 18 may include or may be one ormore processors or processing circuitry, such as one or more digitalsignal processors (DSPs), general purpose microprocessors, applicationspecific integrated circuits (ASICs), field programmable logic arrays(FPGAs), or other equivalent integrated or discrete logic circuitry.Accordingly, the term “processor” and “processing circuitry” as usedherein may refer to any of the foregoing structure or any otherstructure suitable for implementation of the techniques describedherein. In addition, in some examples, the functionality of computingdevice 18 may be provided within dedicated hardware and/or softwaremodules.

In some examples, thermal spray device may include a stage or othercomponent configured to selectively position and restrain substrate 24and/or furnace 14 in place during formation of coating 66. In someexamples, the stage or other component is movable relative to thermalspray device 22. For example, in this manner, substrate 24 may betranslatable and/or rotatable along at least one axis to positionsubstrate 24 relative to plasma spray device 22. Similarly, in someexamples, thermal spray device 22 may be movable relative to substrate24 to position thermal spray device 22 relative to substrate 24.

In one example, system 10 may be configured to form an article such asarticle 66 shown in FIG. 5, which includes EBC system 68 deposited onsubstrate 24. For example, system 10 may be configured to deposit one ormore layers of EBC system 68 on substrate 24 using thermal spray device22, e.g., by air plasma spraying or other thermal spray depositionprocess. Before, during, and/or after the deposition of the one or morelayers of EBC system 68, backside 40 of substrate 24 may be heated viafurnace enclosure 16 to heat frontside surface 42 onto which the one ormore layer is deposited. Computing device 18 may also control theheating of backside 40 via furnace enclosure 16 to control thetemperature of frontside 42 before, during, and/or after the depositionof the one or more layers. In some examples, the heated temperature offrontside 42 is controlled by computing device 18 to provide for anincrease in the amount of crystalline phase to amorphous phase in EBCsystem 68, e.g., as compared to an article in which the EBC system isdeposited by thermal spray device 12 without such heating. In someexamples, the heated temperature of frontside 42 is controlled bycomputing device 18 to provide for a decrease in the porosity of the oneor more layers of EBC system 68, e.g., as compared to an article inwhich the EBC system is deposited by thermal spray device 12 withoutsuch heating.

In some examples, enclosure 20 may be heated separately from that offurnace 12, e.g., to provide a heated environment within enclosure 20.The temperature within enclosure 20 may be controlled by computingdevice 18. In other examples, enclosure 20 may not be separately heated,e.g., such that enclosure 20 is at room temperature or otherwise notheated by a heating source during the spraying process with only furnaceenclosure 16 heating backside 40 of substrate 24 during the sprayingprocess. For example, the only heat source that heats enclosure 20 maybe heat from furnace 12 that heat backside 40, the heat from thedeposited coating material of EBC system 68, and/or heat from theoperation of thermal spray device 22. In such cases, frontside 42 ofsubstrate 24 is only heated through the heating of backside 40 ofsubstrate 24 by furnace enclosure 16, aside from incidental heattransfer from the plume and coating material deposited on frontside 42.In such an example, the relative cost and ease of manufacturing article66 may be reduced by not requiring thermal spray device 22 andassociated components to be contained within a furnace during thethermal spray deposition of EBC system 68 on substrate 24. Rather, insuch examples, substrate 24 is only subject to heating through theheating of backside 40 via furnace enclosure 16.

FIGS. 2A and 2B are conceptual schematic diagrams illustratingcross-sections of furnace 12 and substrate 24 in exploded and assembledviews, respectively. FIGS. 3A and 3B are conceptual schematic diagramsillustrating views of furnace 12 and substrate 24 corresponding to FIGS.2A and 2B, respectively. As shown, furnace 12 include five sidesdefining enclosure 16 with opening 46. Substrate 24 may be located overopening 46 of furnace 12 such that the heating of furnace enclosure 16heats backside 40 of substrate 24 with frontside 42 not being locatedwithin furnace enclosure 16. In some example, substrate 24 may beclosely fit (e.g., interference fit) within opening 46 using aninsulating material to releasably secure substrate 24 within opening 24during thermal spraying, e.g., like that shown in FIG. 6. Depending onthe design of a component, different mechanisms for holding cooler partsof substrate 24 or other insulated holding mechanisms may be employed.

In some examples, like that shown in FIGS. 2B and 3B, substrate 24 has asize and shape that is substantially the same (e.g., the same or nearlythe same) size and shape of opening 46 such that substrate 24substantially covers opening 46 on all sides. In FIGS. 2B and 3B,substrate 24 and opening 46 each have a rectangular shape ofapproximately the same size. In other examples, substrate 24 may have asize and/or shape different from that of the size and/or shape ofopening 46. For example, substrate 24 may be larger than opening 46. Insuch examples, substrate 24 may be positioned to cover opening 24 with aportion of backside 40 and another portion overlapping the perimeter ofopening 24. The portion of backside 40 that covers opening 46 may bedirectly heated by furnace enclosure 16 to heat frontside 42 ofsubstrate 24, e.g., during the thermal spraying of one or more layers ofEBC system 68.

FIG. 5 is a conceptual schematic diagram illustrating article 66 thatmay be formed using system 10 of FIG. 1. In some examples, article 66may include a component of a gas turbine engine. For example, article 66may include a part that forms a portion of a flow path structure, a sealsegment, a blade track, an airfoil, a blade, a vane, a combustionchamber liner, or another portion of a gas turbine engine.

As described herein, article 66 includes EBC system 68 formed onsubstrate 24. EBC system 68 may be a single layer or multi-layercoating, where each layer has substantially the same or differentcompositions. As used herein, “formed on” and “on” mean a layer orcoating that is formed on top of another layer or coating, andencompasses both a first layer or coating formed immediately adjacent asecond layer or coating and a first layer or coating formed on top of asecond layer or coating with one or more intermediate layers or coatingspresent between the first and second layers or coatings. In contrast,“formed directly on” and “directly on” denote a layer or coating that isformed immediately adjacent another layer or coating, e.g., there are nointermediate layers or coatings.

Substrate 24 may include a material suitable for use in ahigh-temperature environment. In some examples, substrate 24 may includea ceramic or a ceramic matrix composite (CMC). Suitable ceramicmaterials, may include, for example, a silicon-containing ceramic, suchas silica (SiO₂) and/or silicon carbide (SiC); silicon nitride (Si₃N₄);alumina (Al₂O₃); an aluminosilicate; a transition metal carbide (e.g.,WC, Mo₂C, TiC); a silicide (e.g., MoSi₂, NbSi₂, TiSi₂); combinationsthereof; or the like. In some examples in which substrate 24 includes aceramic, the ceramic may be substantially homogeneous.

In examples in which substrate 24 includes a CMC, substrate 24 mayinclude a matrix material and a reinforcement material. The matrixmaterial may include, for example, silicon metal or a ceramic material,such as silicon carbide (SiC), silicon nitride (Si₃N₄), analuminosilicate, silica (SiO₂), a transition metal carbide or silicide(e.g., WC, Mo2C, TiC, MoSi₂, NbSi₂, TiSi₂), or another ceramic material.The CMC may further include a continuous or discontinuous reinforcementmaterial. For example, the reinforcement material may includediscontinuous whiskers, platelets, fibers, or particulates.Additionally, or alternatively, the reinforcement material may include acontinuous monofilament or multifilament two-dimensional orthree-dimensional weave, braid, fabric, or the like. In some examples,the reinforcement material may include carbon (C), silicon carbide(SiC), silicon nitride (Si₃N₄), an aluminosilicate, silica (SiO₂), atransition metal carbide or silicide (e.g. WC, Mo₂C, TiC, MoSi₂, NbSi₂,TiSi₂), or the like.

Substrate 12 may be manufactured using one or more techniques including,for example, chemical vapor deposition (CVD), chemical vaporinfiltration (CVI), polymer impregnation and pyrolysis (PIP), slurryinfiltration, melt infiltration (MI), combinations thereof, or othertechniques.

EBC system 68 may help protect underlying substrate 24 from chemicalspecies present in the environment in which article 66 is used, such as,e.g., water vapor, calcia-magnesia-alumina-silicate (CMAS; a contaminantthat may be present in intake gases of gas turbine engines), or thelike. Similarly, the EBC system may also be CMAS resistant, e.g., theEBC system itself may be resistant to damage caused by CMAS. Similarly,EBC system 66 may also be CMAS resistant, e.g., the EBC system itselfmay be resistant to damage caused by CMAS. Additionally, in someexamples, EBC system 68 may also protect substrate 24 and provide forother functions besides that of an EBC, e.g., by functioning as athermal barrier coating (TBC), abradable coating, erosion resistantcoating, and/or the like.

Although not directly shown in FIG. 5, in some examples, article 66 mayinclude a bond coat (e.g., a silicon bond coat) between one or moreoverlaying layers of EBC system 68 and substrate 24, e.g., where thebond coat is directly on substrate 24 and the overlaying layer(s) of EBCsystem 68 are directly on the bond coat. The bond coat may increase theadhesion between substrate 24 and EBC system 68. In some examples, thebond coat has a thickness of approximately 25 microns to approximately250 microns, although other thicknesses are contemplated. In examples inwhich substrate 24 includes a ceramic or CMC, the bond coat may includea ceramic or another material that is compatible with the material fromwhich substrate 12 is formed. For example, the bond coat may includemullite (aluminum silicate, Al₆Si₂O₁₃), silicon metal or alloy, silica,a silicide, or the like. The bond coat may further include otherelements, such as a rare earth silicate including a silicate of lutetium(Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho),dysprosium (Dy), gadolinium (Gd), terbium (Tb), europium (Eu), samarium(Sm), promethium (Pm), neodymium (Nd), praseodymium (Pr), cerium (Ce),lanthanum (La), yttrium (Y), and/or scandium (Sc).

EBC system 68 may include one or more EBC layers, which may beconfigured to help protect substrate 24 against deleteriousenvironmental species, such as CMAS and/or water vapor. The layer(s) ofEBC system 68 may include at least one of a rare-earth oxide, arare-earth silicate, an aluminosilicate, or an alkaline earthaluminosilicate. For example, the layer(s) of EBC system 68 may includemullite, barium strontium aluminosilicate (B SAS), bariumaluminosilicate (BAS), strontium aluminosilicate (SAS), at least onerare-earth oxide, at least one rare-earth monosilicate (RE₂SiO₅, whereRE is a rare-earth element), at least one rare-earth disilicate(RE₂Si₂O₇, where RE is a rare-earth element), or combinations thereof.The rare-earth element in the at least one rare-earth oxide, the atleast one rare-earth monosilicate, or the at least one rare-earthdisilicate may include at least one of lutetium (Lu), ytterbium (Yb),thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium(Gd), terbium (Tb), europium (Eu), samarium (Sm), promethium (Pm),neodymium (Nd), praseodymium (Pr), cerium (Ce), lanthanum (La), yttrium(Y), or scandium (Sc). EBC system 68 may be any suitable thickness. Forexample, EBC system 68 may be about 0.005 inches (about 127 micrometers)to about 0.100 inches (about 2540 micrometers). Other thicknesses arecontemplated.

In some examples, the layer(s) of EBC system 68 additionally andoptionally may include at least one additive, such as at least one ofsilica, a rare earth oxide, alumina, an aluminosilicate, an alkali metaloxide, an alkaline earth metal oxide, an alkali metal aluminosilicate,an alkaline earth aluminosilicate, TiO₂, Ta₂O₅, HfSiO₄, or the like. Theadditive may be added to the EBC to modify one or more desiredproperties of the EBC. For example, the additive components may increaseor decrease the reaction rate of the EBC withcalcia-magnesia-alumina-silicate (CMAS; a contaminant that may bepresent in intake gases of gas turbine engines), may modify theviscosity of the reaction product from the reaction of CMAS andconstituent(s) of the EBC, may increase adhesion of the EBC to the bondcoat, may increase the chemical stability of the EBC, or the like.

FIG. 4 is a flow diagram illustrating an example technique for forming acoating that includes an environmental barrier coating on a substrateusing a thermal spray process. The technique of FIG. 4 will be describedwith respect to system 10 of FIG. 1 and article 66 of FIG. 5 for ease ofdescription only. A person having ordinary skill in the art willrecognize and appreciate that the technique of FIG. 4 may be implementedusing systems other than system 10 of FIG. 1, may be used to formarticles other than article 68 of FIG. 5, or both.

As shown in FIG. 5, substrate 24 may be positioned over opening 46 offurnace enclosure 16, e.g., manually or by a robotic device under thecontrol of computing device 18 (50). When positioned over opening 46, atleast a portion of backside 40 is covering opening 46 with frontsideoutside of opening 46. In some examples, substrate 24 is positioned overopening 46 such that substrate 24 is also positioned for deposition ofone or more layers of EBC system 68 by thermal spray device 22. In otherexamples, furnace 12 and substrate 24 may need to be repositionedrelative to thermal spray device 22 after substrate 24 is located overopening 46 before deposition of the one or more layer of EBC system 68by thermal spraying.

Once substrate 24 is positioned over opening 46, backside 40 may beheated by furnace enclosure 16 under the control of computing device 18to heat frontside 42 of substrate 24 (52). In some examples, computingdevice 18 may heat furnace enclosure 16 so that furnace enclosure 16,backside 40, and/or frontside 42 reaches a desired temperature, asmeasured by temperature sensor 44. The temperature of furnace enclosure16, backside 40, and/or frontside 42 may be selected such that thetemperate of frontside 42 of substrate 24 is elevated above the ambienttemperature of the environment external to furnace 12, e.g., the ambienttemperature within enclosure 20 outside of furnace 12.

In some examples, computing device 18 may heat furnace enclosure 16 to atemperature sufficient to heat frontside 42 of substrate 24 via directheating of backside 40 to a desired elevated temperature. In someexamples, furnace enclosure 16 heats backside 40 such that frontside 42has a temperature of at least about 1000 degrees C., such as, about 1000degrees C. to 1200 degrees C. In some examples, the temperature ofbackside 40 is heated to a temperature of about 1400 degrees C. or lessby furnace enclosure 16, e.g., about 1000 degrees C. to about 1400degrees C.

Once furnace enclosure 16, backside 40, and/or frontside 42 reaches thedesired temperature(s) during the heating process, computing device 18may control thermal spray device 22 and associated components of thermalspray system 10 to deposit one or more layers of EBC system 68 onsubstrate 24 to form article 22. Backside 40 may be heated by furnaceenclosure 16 while the material for the one or more layers is beingdeposited by spray gun 22 to keep frontside 42 at an elevated or desiredtemperature. By elevating the temperature of frontside 42 via backsideheating of substrate 24, the amount of crystalline phase in thedeposited layer(s) may be increased (e.g., compared to instances inwhich frontside 42 is not heated) or otherwise tailored. For example,when a particle is sprayed as a plasma from spray gun 22, the particlemay be in an amorphous phase in air. If the particle hits a relativelycold surface, the particle solidifies relatively quickly, trapping it inthe amorphous state. Conversely, if the substrate is relatively hot(e.g., via backside heating), then the particle has time to crystallize(e.g., which is a preferred lower energy state). This may also give theparticle the opportunity to stay somewhat fluid, allowing for betterinfiltration and fewer pores.

The temperature of frontside 42 during the deposition of the one or morelayers of EBC system 10 may be selected to control at least one of theporosity of the deposited layer(s) or the amount of crystalline phase inthe deposited layer(s) of EBC system 42. For example, the porosity ofthe one or more deposited layers may be less than that of similar layersdeposited using the same process but without heating backside 40 ofsubstrate 24 as described herein. In some example, the temperature offrontside 42 during deposition may be selected to provide the one ormore layers of EBC system 68 with a porosity of, e.g., less than about10% porosity, such as less than about 5% porosity, about 1% to about 10%porosity, about 1% to about 5% porosity, or substantially no pores. AnEBC system with a relatively low porosity (e.g., less than about 10%porosity, such as less than about 5% porosity, about 1% to about 10%porosity, about 1% to about 5% porosity, or substantially no pores) maybe preferred as it may result in improved protection of substrate 24from the environment during high temperature operation.

As another example, the amount (e.g., weight percent) of crystallinephase in the one or more deposited layers may be more than that ofsimilar layers deposited using the same process but without heatingbackside 40 of substrate 24 as described herein. As noted above, withoutheating backside 40, EBC system 68 may have relatively high amount ofamorphous phase. The amorphous phase may change to a crystallinestructure over time when subjected to higher temperatures, e.g., duringoperation of a jet engine. An uncontrolled transition from amorphous tocrystalline structure with time may also result in volumetric changesand, thus, internal stresses in the layer(s). By heating backside 40 ofsubstrate 24, the amount of amorphous phased in EBC system 68 may bedecreased and the amount of crystalline phase may be increased. In someexamples, the one or more deposited layers may have a crystalline phaseof greater than about 50 wt %, such as, greater than about 60 wt %,greater than about 70 wt %, greater than about 80 wt %, greater thanabout 90 wt %, about 50 wt % to about 96 wt % or greater than about 96wt % or about 100 wt %. The remainder of the layer composition may beamorphous phase in some examples. Other values are contemplated.

As shown in FIG. 4, in some examples, article 24 may undergo an optionalpost-deposition heat treatment after the one or more layers of EBCsystem 68 are deposited (56). For instance, in some examples, when EBCsystem 68 is deposited, the layer(s) of system 68 may still have anundesirable amount of amorphous phase in the one or more layers, e.g.,due to the high cooling rates/quenching of the particles upon impactwith substrate 24.

As such, in some examples, following deposition of EBC system 68 onsubstrate 24, article 66 may be heat treated by furnace 12 and/ortransferred to another furnace by robotic transfer device for apost-deposition heat treatment (46). In some examples, thepost-deposition heat treatment may take place before or after article 66cools to room temperature following deposition. The post-deposition heattreatment temperature and duration may be controlled by computing device18 and may be selected to increase the crystalline phase concentrationof EBC system 68 on substrate 24, e.g., compared to that of theas-deposited layer from the thermal spraying. For example, furnaceenclosure 16 may be at a treatment temperature of at or above thecrystalline transition temperature (e.g., the temperature of thetransition between amorphous phase and crystalline phase and/ortemperature of the transition between different crystalline phases) ofthe layer(s) of EBC system 68. Additionally, or alternatively, thepost-deposition heat treatment may reduce the porosity of one or morelayer of EBC system 68.

In some examples, furnace enclosure 14 may be at a treatment temperatureof at least about 1000 degrees C., such as, e.g., about 1000 degrees C.to about 1200 degrees C., or less than about 1400 degrees C. Computingdevice 18 may control furnace 12 to hold a substantially constant heattreatment temperature within furnace or a heat treatment temperaturethat varies within a prescribed range over a selected period of time. Insome examples, during the post-deposition heat treatment, frontside 42of substrate 24 may have a temperature of at least about 1000 degreesC., such as, e.g., about 1000 degrees C. to about 1200 degrees C., orless than about 1400 degrees C.

In some examples, the heat treatment may be controlled such that EBCsystem 68 reaches a temperature at or above the crystalline phasetemperature of the one or more layers of EBC system 68. In someexamples, depending on the composition of the layer(s), the layer(s) ofEBC system 68 may have a temperature of at least about 1000 degrees C.,such as, e.g., about 1000 degrees C. to about 1200 degrees C., or lessthan about 1400 degrees C. Values other than that described above arecontemplated.

Following the post-deposition cooling, article 66 may undergo acontrolled cooling from that of the heat treatment temperature, e.g., bycooling furnace enclosure 14 or by cooling article 66 within anotherfurnace. For example, computing device 18 may control the rate ofcooling of furnace enclosure 14 over a particle period of time such thatarticle 66 cools at a controlled rate over the period of time, ascompared to simply removing article 66 from opening 46 of furnaceenclosure 14 and or simply turning off furnace enclosure 14 whilearticle 66 is positioned over opening 46. By controlling the cooling ofarticle 66 for a period of time following the heat treatment, thecrystalline phase amount in the deposited may be further tailored, e.g.,increased in amount compared to an instance in which article 66 iscooled by removing article 66 from the furnace used for thepost-deposition heat treatment.

In some examples, computing device 18 may control the cooling of article68 such that the temperature of EBC layer 68 cools at a rate of about 10degrees C/minute or less, such as, about 5 degrees C/minute or less,until article 66 is cooled to about 1000 degrees C., followed by furthercooling at a rate up to about 50 degrees C/minute until article 66reaches about 500 degree C. or is approximately equal to roomtemperature.

In some examples, the post deposition heat treatment and/or controlledcooling of article 66 within furnace 14 may be selected to increase thecrystalline phase concentration and/or decrease the amorphous phaseconcentration within EBC system 68 compared to that of the amorphous andcrystalline phase content of EBC system 68 following deposition bythermal spray device 14 but before the heat treatment and/or controlledcooling In some examples, the heat treatment and/or cooling of article66 within furnace 14 may be selected to increase the crystalline phaseconcentration and/or decrease the amorphous phase concentration withinEBC system 68 compared to that of the amorphous and crystalline phasecontent of EBC system 68 following deposition by thermal spray device 14but without any post-deposition heat treatment and/or controlledcooling. In some examples, increasing the crystalline phase content ofthe layer(s) of EBC system 68 may increase the bond strength of EBCsystem 68, e.g., by a factor of approximately two compared to othercoating systems with higher amorphous phase content, and/or increase thethermal cycling stability of EBC system 68.

In some examples, EBC system 68 may have a crystalline phase of greaterthan about 50 wt %, such as, greater than about 60 wt %, greater thanabout 70 wt %, greater than about 80 wt %, greater than about 90 wt %,about 50 wt % to about 96 wt % or greater than about 96 wt % or about100 wt % following the heat treatment describe above and/or thecontroller cooling described above with the remainder, e.g., beingsubstantially all amorphous phase. Other values are contemplated.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware, or any combination thereof.For example, various aspects of the described techniques may beimplemented within one or more processors, including one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs), orany other equivalent integrated or discrete logic circuitry, as well asany combinations of such components. The term “processor” or “processingcircuitry” may generally refer to any of the foregoing logic circuitry,alone or in combination with other logic circuitry, or any otherequivalent circuitry. A control unit including hardware may also performone or more of the techniques of this disclosure.

Such hardware, software, and firmware may be implemented within the samedevice or within separate devices to support the various techniquesdescribed in this disclosure. In addition, any of the described units,modules or components may be implemented together or separately asdiscrete but interoperable logic devices. Depiction of differentfeatures as modules or units is intended to highlight differentfunctional aspects and does not necessarily imply that such modules orunits must be realized by separate hardware, firmware, or softwarecomponents. Rather, functionality associated with one or more modules orunits may be performed by separate hardware, firmware, or softwarecomponents, or integrated within common or separate hardware, firmware,or software components.

The techniques described in this disclosure may also be embodied orencoded in a computer system-readable medium, such as a computersystem-readable storage medium, containing instructions. Instructionsembedded or encoded in a computer system-readable medium, including acomputer system-readable storage medium, may cause one or moreprogrammable processors, or other processors, to implement one or moreof the techniques described herein, such as when instructions includedor encoded in the computer system-readable medium are executed by theone or more processors. Computer system readable storage media mayinclude random access memory (RAM), read only memory (ROM), programmableread only memory (PROM), erasable programmable read only memory (EPROM),electronically erasable programmable read only memory (EEPROM), flashmemory, a hard disk, a compact disc ROM (CD-ROM), a floppy disk, acassette, magnetic media, optical media, or other computer systemreadable media. In some examples, an article of manufacture may compriseone or more computer system-readable storage media.

EXAMPLE

A test was carried out to evaluate one or more aspects of the presentdisclosure. However, the disclosure is not limited by the testing or thecorresponding description.

An open furnace was modified with thermally insulating holder configuredto hold a SiC/SiC CMC substrate over the furnace opening near theheating element. FIG. 6 is a photograph showing the furnace 12,insulating holder 60, and substrate 24. During the test, the heatingelements were taken up to about 1300 degrees C. A pyrometer was used tomeasure the temperature of the frontside surface of substrate 24, e.g.,the surface that would be thermally sprayed (e.g., plasma sprayed) withone or more layers of an EBC system. The surface temperature reachedabout 980 degrees C. with the 1300 degree C. furnace set point. Thus, itwas determined that the backside heating of substrate 24 with furnace 12was capable of heating the frontside of substrate 24 to a desiredtemperature, in some examples.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A method comprising: heating a backside of a substrate using afurnace enclosure, wherein a frontside of the substrate is outside thefurnace enclosure, wherein the heating of the backside of the substratewith the furnace enclosure heats the frontside of the substrate to asurface temperature by heat conduction from the backside of thesubstrate to the frontside of the substrate; and depositing anenvironmental barrier coating (EBC) on the frontside of the substratevia a thermal spray device while the backside of the substrate is heatedusing the furnace enclosure, wherein the surface temperature of thefrontside of the substrate is selected to control at least one of aporosity of the deposited EBC or a weight percent of a crystalline phasein the deposited EBC.
 2. The method of claim 1, wherein heating thebackside of the substrate using the furnace enclosure comprises heatingthe backside of the substrate with the furnace enclosure having afurnace temperature of at about 1000 degrees Celsius to about 1400degrees Celsius.
 3. The method of claim 1, wherein the surfacetemperature of the surface of the frontside is at least about 1000degrees Celsius while the EBC is deposited on the frontside of thesubstrate.
 4. The method of claim 1, wherein the surface temperature ofthe surface of the frontside is at or above a crystalline transitiontemperature of the EBC when the EBC is deposited on the frontside of thesubstrate.
 5. The method of claim 1, wherein the furnace enclosuredefines an opening approximately a size and shape of the substrate,wherein the substrate is located in the opening of the furnace enclosureduring the backside heating such that the backside of the substrate isinside the furnace enclosure and the frontside of the substrate isoutside of the furnace enclosure.
 6. The method of claim 5, wherein thesubstrate substantially covers the opening of the furnace enclosure. 7.The method of claim 1, wherein the frontside of the substrate is notheated by another heating source during the deposition of the EBC on thefrontside.
 8. The method of claim 1, wherein the deposited EBC includesat least about 50 weight percent crystalline phase.
 9. The method ofclaim 1, further comprising heat treating the deposited EBC at or abovea heat treatment temperature for first period of time following thedeposition of the deposited EBC on the substrate.
 10. The method ofclaim 9, wherein the heat-treated EBC includes at least about 96 weightpercent crystalline phase.
 11. A system comprising: a furnace includinga furnace enclosure, wherein the furnace is configured to heat abackside of a substrate using the furnace enclosure while a frontside ofthe substrate is outside the furnace enclosure; a thermal spray device;and a computing device configured to control the furnace to heat thebackside of the substrates using the furnace enclosure to heat thefrontside of the substrate to a surface temperature by heat conductionfrom the backside of the substrate to the frontside of the substrate;and control the thermal spray device to deposit an environmental barriercoating (EBC) on the frontside of the substrate while the backside ofthe substrate is heated using the furnace enclosure, wherein the surfacetemperature of the frontside of the substrate is selected to control atleast one of a porosity of the deposited EBC or a weight percent of acrystalline phase in the deposited EBC.
 12. The system of claim 11,wherein heating the backside of the substrate using the furnaceenclosure comprises heating the backside of the substrate with thefurnace enclosure having a furnace temperature of at about 1000 degreesCelsius to about 1400 degrees Celsius.
 13. The system of claim 11,wherein the surface temperature of the surface of the frontside is atleast about 1000 degrees Celsius while the EBC is deposited on thefrontside of the substrate.
 14. The system of claim 11, wherein thesurface temperature of the surface of the frontside is at or above acrystalline transition temperature of the EBC when the EBC is depositedon the frontside of the substrate.
 15. The system of claim 11, whereinthe furnace enclosure defines an opening approximately a size and shapeof the substrate, wherein the substrate is located in the opening of thefurnace enclosure during the backside heating such that the backside ofthe substrate is inside the furnace enclosure and the frontside of thesubstrate is outside of the furnace enclosure.
 16. The system of claim15, wherein the substrate substantially covers the opening of thefurnace enclosure.
 17. The system of claim 11, wherein the frontside ofthe substrate is not heated by another heating source during thedeposition of the EBC on the frontside.
 18. The system of claim 11,wherein the deposited EBC includes at least about 50 weight percentcrystalline phase.
 19. The system of claim 11, further comprising heattreating the deposited EBC at or above a heat treatment temperature forfirst period of time following the deposition of the deposited EBC onthe substrate.
 20. The system of claim 19, wherein the heat-treated EBCincludes at least about 96 weight percent crystalline phase.